Broadband amplifier and communication system

ABSTRACT

A method of broadband amplification divides an optical signal of wavelength of 1430 nm to 1620 nm at a preselected wavelength into a first beam and a second beam. The first beam is directed to at least one optical amplifier and produces an amplified first beam. The second beam is directed to at least one rare earth doped fiber amplifier to produce an amplified second beam. The first and second amplified beams are combined.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Pat. No. 6,356,384, Ser No.09/547,165, filed Apr. 11, 2000, which is a continuation-in-part of U.S.Pat. No. 6,101,024, Ser. No. 09/046,900, filed Mar. 24, 1998, and acontinuation-in-part of Ser. No. 09/470,831, filed Dec. 23, 1999, nowabandoned all of which are fully incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates generally to broadband amplifiers andcommunication systems, and more particularly to broadband boosteramplifiers and communication systems with Raman and rare-earth dopedamplifiers.

2. Description of Related Art

Because of the increase in data intensive applications, the demand forbandwidth in communications has been growing tremendously. In response,the installed capacity of telecommunication systems has been increasingby an order of magnitude every three to four years since the mid 1970s.Much of this capacity increase has been supplied by optical fibers thatprovide a four-order-of-magnitude bandwidth enhancement overtwisted-pair copper wires.

To exploit the bandwidth of optical fibers optical amplifiers andwavelength-division multiplexing (WDM) have been developed and utilizedin optical communications. Optical amplifiers boost the signal strengthand compensate for inherent fiber loss and other splitting and insertionlosses. WDM enables different wavelengths of light to carry differentsignals parallel over the same optical fiber. Although WDM is criticalin that it allows utilization of a major fraction of the fiberbandwidth, it would not be cost-effective without optical amplifiers. Inparticular, a broadband optical amplifier that permits simultaneousamplification of many WDM channels is a key enabler for utilizing thefull fiber bandwidth.

Silica-based optical fiber has its lowest loss window around 1550 nmwith approximately 25 THz of bandwidth between 1430 and 1620 nm. In thiswavelength region, erbium-doped fiber amplifiers (EDFAs) are widelyused. However, the absorption band of a EDFA nearly overlaps its theemission band. For wavelengths shorter than about 1525 nm, erbium-atomsin typical glasses will absorb more than amplify. To broaden the gainspectra of EDFAs, various dopings have been added. Co-doping of thesilica core with aluminum or phosphorus broadens the emission spectrumconsiderably. Nevertheless, the absorption peak for the various glassesis still around 1530 nm.

Broadening the bandwidth of EDFAs to accommodate a larger number of WDMchannels has become a subject of intense research. A two-bandarchitecture for an ultra-wideband EDFA has been developed with anoptical bandwidth of 80 nm. To obtain a low noise figure and high outputpower, the two bands share a common first gain section and have distinctsecond gain sections. The 80 nm bandwidth comes from one amplifier(so-called conventional band or C-band) from 1525.6 to 1562.5 nm andanother amplifier (so-called long band or L-band) from 1569.4 to 1612.8nm.

These recent developments illustrate several points in the search forbroader bandwidth amplifiers for the low-loss window in optical fibers.First, even with EDFAs, bandwidth in excess of 40-50 nm requires the useof parallel combination of amplifiers. Second, the 80 nm bandwidth maybe very close to the theoretical maximum. The short wavelength side atabout 1525 nm is limited by the inherent absorption in erbium, and longwavelength side is limited by bend-induced losses in standard fibers atabove 1620 nm. Therefore, even with these recent advances, half of thebandwidth of the low-loss window, i.e., 1430-1530 nm, remains without anoptical amplifier.

There is a need for a broadband amplifier and broadband communicationsystem suitable for a wide range of wavelengths.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a methodof broadband amplification that divides an optical signal with awavelength of 1430 nm to 1620 nm at a preselected wavelength into afirst beam and a second beam.

Another object of the present invention is to provide a method ofbroadband communication that propagates a plurality of WDM wavelengths,with at least a portion of the WDM wavelengths in the range of 1430 to1530 nm, from a transmitter assembly along a transmission line.

Yet another object of the present invention is to provide a method ofbroadband communication that propagates a first plurality of WDMwavelengths in the wavelength range of 1530 to 1620 from a transmitterassembly along a transmission line, and introduces a second plurality ofWDM wavelengths in the wavelength range of 1430 to 1530 to thetransmission line.

In another embodiment of the present invention, a method of broadbandamplification divides an optical signal of wavelength of 1430 nm to 1620nm at a preselected wavelength into a first beam and a second beam. Thefirst beam is directed to at least one optical amplifier and produces anamplified first beam. The second beam is directed to at least one rareearth doped fiber amplifier to produce an amplified second beam. Thefirst and second amplified beams are combined.

In another embodiment of the present invention, a method transmittingWDM wavelengths in a broadband communication system includes propagatinga plurality of WDM wavelengths from a transmitter assembly along atransmission line. At least a portion of the WDM wavelengths are in thewavelength range of 1430 to 1530 nm. At least a portion of the pluralityof wavelengths are amplified with a Raman amplifier assembly to create aplurality of amplified WDM wavelengths. The plurality of amplified VDMwavelengths are received at a receiver assembly.

In another embodiment, a method of transmitting WDM wavelengthspropagates a first plurality of WDM wavelengths in the wavelength rangeof 1530 to 1620 from a transmitter assembly along a transmission line. Asecond plurality of WDM wavelengths in the wavelength range of 1430 to1530 is introduced to the transmission line; The second plurality of WDMwavelengths are amplified by Raman amplification after the secondplurality of WDM wavelengths are introduced to the transmission line.The first and second pluralities of WDM wavelengths are received at areceiver assembly.

In another embodiment of the present invention, a method of transmittingWDM wavelengths in a broadband communication system includes,propagating a plurality of WDM wavelengths from a transmitter assemblyalong a transmission line. At least a portion of the plurality of WDMwavelengths are in the wavelength range of 1430 to 1530 nm. A portion ofthe plurality of wavelengths are amplified with a Raman amplifierassembly to create a plurality of amplified WDM wavelengths that arereceived at a receiver assembly.

In another embodiment of the present invention, a method of transmittingWDM wavelengths in a broadband communication system includes propagatinga first plurality of WDM wavelengths in the wavelength range of 1530 to1620 from a transmitter assembly along a transmission line. A secondplurality of WDM wavelengths in the wavelength range of 1430 to 1530 areintroduced to the transmission line. The second plurality of WDMwavelengths are amplified by Raman amplification after the secondplurality of WDM wavelengths are introduced to the transmission line.The first and second pluralities of WDM wavelengths are received at areceiver assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a schematic diagram of one embodiment of a broadbandamplifier of the present invention with a parallel geometric combinationof Raman and rare-earth doped amplifiers.

FIG. 1(b) is a schematic diagram of another embodiment of a broadbandamplifier of the present invention with a parallel geometric combinationof Raman and rare-earth doped amplifiers.

FIG. 2(a) is a graph illustrating that transmission of any two bandsfrom the parallel geometric combinations of the Raman and rare-earthamplifiers of FIGS. 1(a) and 1(b) is a function of wavelength ofcombiners splitters.

FIG. 2(b) is a graph illustrating that transmission of the C or L bandand the S band from the parallel geometric combinations of the Raman andrare-earth amplifiers of FIGS. 1(a) and 1(b) is a function of wavelengthof combiners splitters.

FIG. 3(a) is a schematic diagram of one embodiment of a broadbandbooster amplifier of the present invention.

FIG. 3(b) is a schematic diagram of another embodiment of a broadbandbooster amplifier of the present invention.

FIG. 4(a) is a schematic diagram of one embodiment of a broadbandpre-amplifier of the present invention.

FIG. 4(b) is a schematic diagram of another embodiment of a broadbandpre-amplifier of the present invention.

FIGS. 5(a) through 11(b) are schematic diagrams illustrating differentembodiments of broadband communication systems of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In various embodiments, the present invention provides parallel opticalamplification with a combination of optical amplifiers. This parallel isoptical amplification can include two parallel stages of Raman andrare-earth doped optical amplifiers.

Referring now to FIGS. 1(a) and 1(b), Amplifier 10 (FIG. 1(a)) andamplifier 11 (FIG. 1(b)) each include at least one input fiber 12coupled to a splitter 14. Examples of splitters include WDM couplers,fused tapered couplers, Mach-Zehnder interferometers, gratings andcirculators, and the like. Splitter 14 divides an optical signal havinga wavelength between 1430 nm and 1620 nm at a predetermined wavelength,preferably at 1525 nm, into at least a first wavelength and a secondwavelength. A Raman amplifier 16 and a rare-earth doped opticalamplifier 18 are coupled to splitter 14 and arranged in a parallelmanner. Raman amplifier 16 receives the first band and produces anamplified broadband first band. Rare-earth doped optical amplifier 18receives the second band and produces an amplified broadband secondband.

A combiner 20 is coupled to Raman amplifier 16 and rare-earth dopedoptical amplifier 18. Combiner 20 combines the amplified and spectrallybroadened first and second bands to produce an amplified broadbandoptical signal. A transition from a stop band to a pass band of combiner20 occurs in preferably 20 nm or less, more preferably 15 nm or less andmost preferably 10 nm or less. An output fiber 22 is coupled to combiner20. Preferably splitter 14 and combiner 20 are WDM couplers. An outputfiber 22 is coupled to combiner 20.

In one embodiment, input fiber 12 transmits at least a first wavelengthand a second wavelength. The first wavelength falls within a gainbandwidth of Raman amplifier 16 and the second wavelength falls within again bandwidth of rare-earth doped optical amplifier 18.

A gain tilt control device 24 can be coupled to splitter 14, Ramanamplifier 16, rare-earth doped optical amplifier 18 or combiner 20.Suitable gain tilt control devices 24 include but are not limited toadjustable gain flattening filters, long period gratings, cascadedMach-Zehnder filters, acousto-optic filter devices and the like.

In FIG. 1(a) Raman amplifier 16 and rare-earth doped amplifier 18 arearranged so that the first and second bands co-propagate In FIG. 1(b),Raman amplifier 16 and rare-earth doped amplifier 18 are arranged sothat the first and second bands are counter-propagating. Thecounter-propagating reduces interaction between the first and secondbands.

FIGS. 2(a) and 2(b) illustrate that in parallel geometric combinationsof Raman amplifier 16 and rare-earth doped amplifier 18 transmission ofthe two bands is a function of wavelength of combiner 20 and splitter14. FIG. 2(a) is generic for any two bands while FIG. 2(b) is specificto the S and C/L bands.

FIGS. 3(a) and 3(b) illustrate broadband booster amplifier 30embodiments of the present invention that include a first plurality oftransmitters 32 that emits a first plurality of wavelengths, and asecond plurality of transmitters 34 that transmit a second band ofwavelengths. Raman amplifier 16 is coupled to the second plurality oftransmitters 34 through a combiner 38. Raman amplifier 16 amplifies thefirst band of wavelengths. Rare-earth doped optical amplifier 18 iscoupled to the plurality of transmitters 32 through a combiner 36.Rare-earth doped optical amplifier 18 amplifies the second band ofwavelengths. Combiner 20 is coupled to Raman amplifier 16 and rare-earthdoped optical amplifier 18. Combiner 20 combines an optical signal fromRaman amplifier 16 and rare-earth doped amplifier 18 into at least afirst wavelength and a second wavelength. A transition from a stop bandto a pass band of combiner 20 occurs preferably in 20 nm or less, morepreferably 15 nm or less and still more preferably 10 nm or less. Outputfiber 22 is coupled to combiner 20. Gain tilt control device 24 can becoupled to Raman amplifier 16, rare-earth doped optical amplifier 18 orcombiner 20. In FIG. 3(b), rare-earth doped amplifier 18 is coupled tocombiner 20. Raman amplifier 16 is coupled to a combiner 40.

In FIG. 3(a) Raman amplifier 16 and rare-earth doped amplifier 18 arearranged so that the first and second bands co-propagate. In FIG. 3(b),Raman amplifier 16 and rare-earth doped amplifier 18 are arranged sothat the first and second bands are counter-propagating.

FIGS. 4(a) and 4(b) illustrate broadband pre-amplifier 42 embodiments ofthe present invention that include at least one input fiber 12 coupledto splitter 14. Splitter 14 splits an optical signal into at least afirst wavelength and a second wavelength, wherein a transition from astop band to a pass band of the splitter occurs preferably in 20 nm orless, more preferably 15 nm or less and still more preferably in 10 nmor less. Raman amplifier 16 and rare-earth doped optical amplifier arecoupled to splitter 14. A splitter 44 is coupled to a first plurality ofreceivers 46 and rare-earth doped optical amplifier 18. A splitter 48 iscoupled to a second plurality of receivers 50 and Raman amplifier 18. InFIG. 4(b), rare-earth doped amplifier 18 is coupled to combiner 20.Raman amplifier 16 is coupled to combiner 52.

In FIG. 4(a) Raman amplifier 16 and rare-earth doped amplifier 18 arearranged so that the first and second bands co-propagate. In FIG. 4(b),Raman amplifier 16 and rare-earth doped amplifier 18 are arranged sothat the first and second bands are counter-propagating.

In the embodiments illustrated in FIGS. 1(a) through 4(b), Ramanamplifier 16 can be optimized for wavelengths between 1430 to 1530 nm.Rare-earth doped optical amplifier 18 can be optimized for wavelengthsbetween 1530 to 1620 nm. Rare-earth doped optical amplifier 18 ispreferably doped with erbium, thulium, telluride, preseodenium.

Additional elements can be included with any of the amplifiers 10 and 11of FIG. 1(a) through FIG. 4(b). Such elements include but not limited togain equalizers, add/drop multiplexers, dispersion compensating elementsand the like, all of which can be positioned in and around theamplifier. Suitable gain equalizers include but are not limited to longperiod gratings, Mach-Zehnder interferometer filters, dielectric filtersand the like. Suitable add/drop multiplexers include but are not limitedto gratings and circulators, gratings in Mach-Zehnder interferometersand dielectric filters. Suitable dispersion compensating elementsinclude but are not limited chirped gratings and circulators anddispersion compensating fibers. Amplifiers 10 and 11 can be included inmulti-stage sub-systems, have more than two amplifiers in parallelconfigurations and be discrete or distributed amplifiers.

The present invention is also a broadband communication system.Referring now to FIGS. 5(a) and 5(b), amplifiers 10 and 11 can becoupled with any type of transmitter and receiver. As illustrated,broadband communication system 54 includes a transmitter 56 coupled toinput fiber 12. A receiver 58 is coupled to output fiber 22 which inturn is coupled to combiner 20. Transmitter 56 can be a semiconductorlaser as well as other types of lasers and devices that emitwavelengths. Receiver 58 can be a detector coupled with electroniccircuitry. In FIG. 5(a) Raman amplifier 16 and rare-earth doped opticalamplifier 18 are arranged so that the first and second bandsco-propagate, while in FIG. 5(b) they are arranged so that the first andsecond bands counter-propagate.

FIGS. 6(a) and 6(b) illustrate other embodiments of broadbandcommunication systems 60 and 62, respectively with in-line amplifierscoupled to transmitter and receiver assemblies. Broadband communicationsystem 60 includes broadband amplifier 10 coupled to a transmitterassembly 64 and a receiver assembly 66. Transmitter assembly 64 includesa first plurality of transmitters 68 that emits a first band ofwavelengths, and a second plurality of transmitters 70 that transmit asecond band of wavelengths each coupled to a combiner 72 and 74,respectively. The first and second bands co-propagate. Combiners 72 and74 in turn are coupled to a combiner 76. Combiner 76 is coupled tobroadband amplifier 10. Receiver assembly 66 includes a first pluralityof receivers 78 and a second plurality of receivers 80, each coupled toa splitter 82 and 84, respectively. Splitters 82 and 84 are coupled to asplitter 86 which is then coupled to broadband amplifier 10.

In FIG. 6(b), amplifier 11 is coupled to a transmitter/receiver assembly88 and a transmitter receiver assembly 90. Transmitter/receiver assembly88 includes a first plurality of transmitters 92 coupled to a combiner94. First plurality of transmitters 92 emits a first band ofwavelengths. A first plurality of receivers 96 is coupled to a splitter98. Combiner 94 and splitter 98 are coupled to a combiner 100 which inturn is coupled to amplifier 11. Transmitter/receiver assembly 90includes a second plurality of receivers 102 coupled to a splitter 104and a second plurality of transmitters 106 that transmit a second bandof wavelengths. Second plurality of transmitters 106 is coupled to acombiner 108. Splitter 104 and combiner 108 are coupled to a splitter110 which in turn is coupled to broadband amplifier 11. In theembodiment of FIG. 6(b) the two bands counter-propagate.

As illustrated in FIGS. 7(a) and 7(b) booster amplifiers are connectedto a transmission line and a receiver assembly. A broadbandcommunication system 112, illustrated in FIG. 7(a) includes broadbandbooster amplifier 30 coupled to receiver assembly 66. In thisembodiment, the first and second bands co-propagate.

Broadband communication system 114, illustrated in FIG. 7(b) includesbroadband booster amplifier 30 coupled to splitter 98 and splitter 104.First plurality of receivers 96 is coupled to splitter 98. Secondplurality of receivers 102 is coupled to splitter 104. Splitter 98 iscoupled to combiner 20, and splitter 104 is coupled to combiner 40. Thetwo bands of broadband communication system 114 counter-propagate.

FIGS. 8(a) and 8(b) illustrate pre-amplifiers connected to atransmission line and a transmitter assembly. Broadband communicationsystem 116, illustrated in FIG. 8(a) includes transmitter assembly 64which is coupled to broadband pre-amplifier 42. The first and secondband co-propagate.

Broadband communication system 118, illustrated in FIG. 8(b) includesfirst plurality of transmitters 120 which transmit a first band ofwavelengths. First plurality of transmitters 120 is coupled to acombiner 122. A second plurality of transmitters 124 transmit a secondband of wavelengths. Second plurality of transmitters 124 is coupled tocombiner 126. Combiner 122 and combiner 126 are each coupled tobroadband amplifier 42. The two bands counter-propagate with broadbandcommunication system 118.

Referring to FIGS. 9(a) and 9(b) a booster amplifier and an in-lineamplifier are connected to a transmission line and a receiver assembly.Broadband communication system 128, illustrated in FIG. 9(a), includes abooster/amplifier assembly 130 and receiver assembly 66, each coupled toamplifier 10. Booster/amplifier assembly 130 includes a first pluralityof transmitters 132, a combiner 134, a rare-earth doped amplifier 136, asecond plurality of transmitters 138, a combiner 140, a Raman amplifier142 and a combiner 144. First plurality of transmitters 132 emits afirst band of wavelengths, and second plurality of transmitters 138emits a second band of wavelengths. The first and second band ofwavelengths co-propagate. Combiner 144 and splitter 86 are each coupledto amplifier 10.

Broadband communication system 146, illustrated in FIG. 9(b), includes arare-earth doped amplifier 148 coupled to transmitter/receiver assembly88. Also included is a Raman amplifier 150 coupled totransmitter/receiver assembly 90. Combiner 100 and splitter 110 are eachcoupled to amplifier 11. The first and second bands counter-propagatewith broadband communication system 146.

Referring now to FIGS. 10(a) and 10(b), pre-amplifiers and in-lineamplifiers are connected to transmission lines and transmitterassemblies. In FIG. 10(a) a broadband communication system 152 includestransmitter assembly 64 and a receiver assembly 154 that are bothcoupled to amplifier 10. Receiver assembly 154 includes a splitter 156,a rare-earth doped amplifier 158, a Raman amplifier 160, splitters 162and 164 as well as first and second pluralities of receivers 166 and168. Rare-earth doped amplifier 158 is coupled to splitters 156 and 162.Raman amplifier 160 is coupled to splitters 156 and 164. The first andsecond bands co-propagate.

Broadband communication system 170, illustrated in FIG. 10(b), includesa Raman amplifier 172 coupled to transmitter/receiver assembly 88. Ramanamplifier 172 is coupled to splitter 98 and combiner 100. A rare earthdoped optical amplifier 174 is coupled to transmitter/receiver assembly90. Rare-earth doped optical amplifier 174 is coupled to splitters 104and 110. Splitter 110 and combiner 100 are each coupled to amplifier 11.The first and second bands counter-propagate.

In FIGS. 11(a) and 11(b), a booster amplifier, in-line amplifier andpreamplifier are connected to a transmission line. Broadbandcommunication system 176, illustrated in FIG. 11(a), includes arare-earth doped amplifier 178 and a Raman amplifier 180 that arecoupled to transmitter assembly 64. Rare-earth doped amplifier 178 iscoupled to combiners 72 and 76. Raman amplifier 180 is coupled tocombiners 74 and 76. Combiner 76 is coupled to splitter 14 of amplifier10. Receiver assembly 154 is coupled to combiner 20 of amplifier 10. Arare-earth doped amplifier 182 and a Raman amplifier 184 are coupled toreceiver assembly 66. Rare-earth doped optical amplifier 182 is coupledto splitters 86 and 82. Raman amplifier 184 is coupled to splitters 84and 86. Splitter 86 and combiner 76 are coupled to amplifier 10. Thefirst and second bands co-propagate.

Referring now to FIG. 11(b), a broadband communication system 186includes a rare-earth doped optical amplifier 178 and Raman amplifier180 coupled to transmitter/receiver assembly 88. Rare-earth dopedoptical amplifier 178 is coupled to combiners 94 and 100. Ramanamplifier 180 is coupled to splitter 98 and combiner 100. Rare-earthdoped amplifier 182 and Raman amplifier 184 are coupled totransmitter/receiver assembly 90. Rare-earth doped optical amplifier iscoupled to splitters 104 and 110. Raman amplifier 184 is coupled tocombiner 108 and splitter 110. Splitter 110 and combiner 100 are coupledto amplifier 11. The first and second bands counter-propagate.

The broadband communication systems illustrated in FIGS. 5(a) through11(b) can employ a variety of different optical fibers including but notlimited to standard fiber, DSF, non-zero dispersion shifted fiber(NZ-DSF), and the like. Standard fiber has a zero dispersion wavelengthnear 1310 nm. The zero dispersion wavelength of DSF is near 1550 nm.NZ-DSF has different zero dispersion wavelengths, depending on themanufacturer. The broadband communication systems of the presentinvention can designed to be dispersion managed systems with fibers thathave different amounts of dispersion spliced together to make a systemthat has locally high dispersion and globally low dispersion. Further,the broadband communication systems of the present invention haveutility in undersea cable systems, wide area networks (WAN),metropolitan area networks (MAN) and local area networks (LAN).Switches, cross-connects, routers, restoration switches and add/dropmultiplexers can be included with any of the broadband communicationsystems of the present invention.

The present invention is also a method of broadband amplification thatuses any of the FIG. 1(a) through FIG. 11(b) amplifiers or systems. Inthis embodiment, an optical signal of wavelength of 1430 nm to 1620 nmis divided at a preselected wavelength into a first beam and a secondbeam. The first beam is directed to at least one optical amplifier andproduces an amplified first beam. The second beam is directed to atleast one rare earth doped fiber amplifier to produce an amplifiedsecond beam. The first and second amplified beams are combined.

In another embodiment of the present invention, a method of transmittingWDM wavelengths, in any of the FIG. 5(a) through FIG. 11(b) broadbandcommunication systems, includes propagating a plurality of WDMwavelengths from a transmitter assembly along a transmission line. Atleast a portion of the WDM wavelengths are in the wavelength range of1430 to 1530 nm. At least a portion of the plurality of wavelengths areamplified with a Raman amplifier assembly to create a plurality ofamplified WDM wavelengths. The plurality of amplified WDM wavelengthsare received at a receiver assembly. At least a portion of the WDMwavelengths can be in the wavelength range of 1530 to 1570 nm, 1570 to1630 nm or both.

In another embodiment of the present invention, a method of transmittingWDM wavelengths, in any of the FIG. 5(a) through FIG. 11(b) broadbandcommunication systems, propagates a first plurality of WDM wavelengthsin the wavelength range of 1530 to 1620 from a transmitter assemblyalong a transmission line. A second plurality of WDM wavelengths in thewavelength range of 1430 to 1530 is introduced to the transmission line.The second plurality of WDM wavelengths are amplified by Ramanamplification after the second plurality of WDM wavelengths areintroduced to the transmission line. The first and second pluralities ofWDM wavelengths are received at a receiver assembly.

In another embodiment of the present invention, a method of transmittingWDM wavelengths, in any of the FIG. 5(a) through FIG. 11(b) broadbandcommunication systems, propagates a plurality of WDM wavelengths from atransmitter assembly along a transmission line. At least a portion ofthe plurality of WDM wavelengths are in the wavelength range of 1430 to1530 nm. A portion of the plurality of wavelengths are amplified with aRaman amplifier assembly to create a plurality of amplified WDMwavelengths that are received at a receiver assembly.

In another embodiment of the present invention, a method of transmittingWDM wavelengths, in any of the FIG. 5(a) through FIG. 11(b) broadbandcommunication systems, propagates a first plurality of WDM wavelengthsin the wavelength range of 1530 to 1620 from a transmitter assemblyalong a transmission line. A second plurality of WDM wavelengths in thewavelength range of 1430 to 1530 are introduced to the transmissionline. The second plurality of WDM wavelengths are amplified by Ramanamplification after the second plurality of WDM wavelengths areintroduced to the transmission line. The first and second pluralities ofWDM wavelengths are received at a receiver assembly. The transmissionline can be coupled to a Raman amplifier assembly that Raman amplifiesthe second plurality of WDM wavelengths.

In the methods of the present invention, the transmission can have amagnitude of dispersion of at least 5 ps/(nm)(km), be in the range of1-5 ps/(nm)(km) or be less than 1 ps/(nm)(km). Raman amplifierassemblies of the methods of the present invention can include adiscrete Raman amplifier inserted into the transmission line. The Ramanamplifier assembly can include a distributed Raman amplifier and adiscrete Raman amplifier. Additionally, the Raman amplifier assembly caninclude a dispersion compensating fiber with a magnitude of dispersionof at least 50 ps/(nm)(km). At least a portion of the gain of the Ramanamplifier assembly can be in the dispersion compensating fiber.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention.

What is claimed is:
 1. A method of communicating WDM wavelengths in abroadband communication system, comprising: receiving a plurality of WDMwavelengths at a transmission line; amplifying at least a portion of theplurality of WDM wavelengths with a Raman amplifier assembly thatincludes a distributed Raman amplifier and a discrete Raman amplifier tocreate a plurality of amplified WDM wavelengths, at least a portion ofthe amplifier assembly including a dispersion compensating fiber with amagnitude of dispersion of at least 50 ps/(nm)(km) for at least aportion of the plurality of WDM wavelengths; and receiving the pluralityof amplified WDM wavelengths at a receiver assembly.
 2. The method ofclaim 1, wherein at least a portion of the WDM wavelengths are in thewavelength range of 1530 to 1570 nm.
 3. The method of claim 1, whereinat least a portion of the WDM wavelengths are in the wavelength range of1570 to 1630 nm.
 4. The method of claim 1, wherein a first portion ofthe WDM wavelengths are in the wavelength range of 1530 to 1570 nm and asecond portion of the WDM wavelengths are in the wavelength range of1570 to 1630 nm.
 5. The method of claim 1, wherein the transmission linehas a magnitude of dispersion of at least 5 ps/(nm)(km) forsubstantially all of the plurality of WDM wavelengths.
 6. The method ofclaim 1, wherein the transmission line as a magnitude of dispersion inthe range of 1-5 ps/(nm)(km) for at least a portion of the plurality ofWDM wavelengths.
 7. The method of claim 1, wherein the transmission linehas a magnitude of dispersion less than 1 ps/(nm)(km) for at least aportion of the plurality of WDM wavelengths.
 8. A method ofcommunicating WDM wavelengths in a broadband communication system,comprising: receiving a plurality of WDM wavelengths at a transmissionline, at least a portion of the transmission line having a magnitude ofdispersion of at least 5 ps/(nm)(km) for at least a portion of theplurality of WDM wavelengths; amplifying at least a portion of theplurality of WDM wavelengths with a Raman amplifier assembly thatincludes a serial combination of a distributed Raman amplifier and adiscrete Raman amplifier to create a plurality of amplified WDMwavelengths; and receiving the plurality of amplified WDM wavelengths ata receiver assembly; wherein a majority of the plurality of WDMwavelengths received by each of the distributed Raman amplifier and thediscrete Raman amplifier are also received by the other of thedistributed Raman amplifier and the discrete Raman amplifier, andwherein all WDM wavelengths amplified by the discrete Raman amplifierare received by the same gain medium within the discrete Ramanamplifier.
 9. The method of claim 8, wherein at least a portion of theWDM wavelengths are in the wavelength range of 1530 to 1570 nm.
 10. Themethod of claim 8, wherein at least a portion of the WDM wavelengths arein the wavelength range of 1570 to 1630 nm.
 11. The method of claim 8,wherein a first portion of the WDM wavelengths is in the wavelengthrange of 1530 to 1570 nm and a second portion of the WDM wavelengths isin the wavelength range of 1570 to 1630 nm.
 12. The method of claim 8,wherein at least a portion of the amplifier assembly includes adispersion compensating fiber.
 13. The method of claim 12, wherein atleast a portion of the dispersion Compensating fiber has a magnitude ofdispersion of at least 50 ps/(nm)(km) for at least a portion of theplurality of WDM wavelengths.
 14. A method of communicating WDMwavelengths in a broadband communication system, comprising: receiving aplurality of WDM wavelengths at a transmission line, at least a portionof the transmission line having a magnitude of dispersion of less than 5ps/(nm)(km) for at least a portion of the plurality of WDM wavelengths;amplifying at least a portion of the plurality of WDM wavelengths with aRaman amplifier assembly that includes a serial combination of adistributed Raman amplifier and a discrete Raman amplifier to create aplurality of amplified WDM wavelengths, and receiving the plurality ofamplified WDM wavelengths at a receiver assembly; wherein a majority ofthe plurality of WDM wavelengths received by each of the distributedRaman amplifier and the discrete Raman amplifier are also received bythe other of the distributed Raman amplifier and the discrete Ramanamplifier, and wherein all WDM wavelengths amplified by the discreteRaman amplifier are received by the same gain medium within the discreteRaman amplifier.
 15. The method of claim 14, wherein at least a portionof the WDM wavelengths are in the wavelength range of 2530 to 2570 nm.16. The method of claim 14, wherein at least a portion of the WDMwavelengths are in the wavelength range of 1570 to 1630 nm.
 17. Themethod of claim 14, wherein a first portion of the WDM wavelengths is inthe wavelength range of 1530 to 1570 nm and a second portion of the WDMwavelengths is in the wavelength rage of 1570 to 1630 nm.
 18. The methodof claim 14 wherein at least a portion of the amplifier assemblyincludes a dispersion compensating fiber.
 19. The method of claim 18,wherein at least a portion of the dispersion compensating fiber has amagnitude of dispersion of at least 50 ps/(nm)(km) for at least aportion of the plurality of WDM wavelengths.
 20. A method ofcommunicating WDM wavelengths in a broadband communication system,comprising: receiving a plurality of WDM wavelengths at a transmissionline; amplifying at least a portion of the plurality of WDM wavelengthswith a Raman amplifier assembly that includes a serial combination of adistributed Raman amplifier and a discrete Raman amplifier to create aplurality of amplified WDM wavelengths, wherein at least a portion ofthe WDM wavelengths are in the wavelength range of 1530 to 1630 nm, andwherein a majority of the plurality of WDM wavelengths received by eachof the distributed Raman amplifier and the discrete Raman amplifier arealso received by the other of the distributed Raman amplifier and thediscrete Raman amplifier, and wherein all wavelengths amplified by thediscrete Raman amplifier are received by the same gain medium within thediscrete Raman amplifier; and receiving the plurality of amplified WDMwavelengths at a receiver assembly.
 21. The method of claim 20, whereinthe transmission line has a magnitude of dispersion of at least 5ps/(nm)(km) for substantially all of the plurality of WDM wavelengths.22. The method of claim 20, wherein the transmission line has amagnitude of dispersion in the range of 1-5 ps/(nm)(km) for at least aportion of the plurality of WDM wavelengths.
 23. The method of claim 20,wherein the transmission line has a magnitude of dispersion less than 1ps/(nm)(km) for at least a portion of the plurality of WDM wavelengths.24. The method of claim 20, wherein at least a portion of the amplifierassembly includes a dispersion compensating fiber.
 25. The method ofclaim 24, wherein at least a portion of the dispersion compensatingfiber has a magnitude of dispersion of at least 50 ps/(nm)(km) for atleast a portion of the plurality of WDM wavelengths.
 26. A method ofcommunicating WDM wavelengths in a broadband communication system,comprising: receiving a plurality of WDM wavelengths; amplifying atleast a portion of the plurality of WDM wavelengths to create aplurality of amplified WDM wavelengths with a Raman amplifier assemblythat includes a gain control device and a serial combination of adistributed Raman amplifier and a discrete Raman amplifier; and whereina majority of the plurality of WDM wavelengths received by each of thedistributed Raman amplifier and the discrete Raman amplifier are alsoreceived by the other of the distributed Raman amplifier and thediscrete Raman amplifier, and wherein all wavelengths amplified by thediscrete Raman amplifier are received by the same gain medium within thediscrete Raman amplifier.
 27. The method of claim 26, wherein the gaincontrol device includes at least one adjustable gain flattening filter.28. The method of claim 26, wherein the gain control device includes atleast one long period grating.
 29. The method of claim 26, wherein thegain control device includes at least one cascaded Mach-Zehnder filter.30. The method of claim 26, wherein the gain control device includes atleast one acousto-optic filter device.
 31. The method of claim 26,wherein at least a portion of the WDM wavelengths are in the wavelengthrange of 1530 to 1570 nm.
 32. The method of claim 26, wherein at least aportion of the WDM wavelengths are in the wavelength range of 1570 to1630 nm.
 33. The method of claim 26, wherein a first portion of the WDMwavelengths are in the wavelength range of 1530 to 1570 nm and a secondportion of the WDM wavelengths arc in the wavelength range of 1570 to1630 nm.
 34. The method of claim 26, wherein the plurality of WDMwavelengths are received from a transmission line comprising a magnitudeof dispersion of at least 5 ps/(nm)(km) for substantially all of theplurality of WDM wavelengths.
 35. The method of claim 26, wherein theplurality of WDM wavelengths are received from a transmission linecomprising a magnitude of dispersion in the range of 1-5 ps/(nm)(km) forat least a portion of the plurality of WDM wavelengths.
 36. The methodof claim 26, wherein the plurality of WDM wavelengths are received froma transmission line comprising a magnitude of dispersion less than 1ps/(nm)(km) for at least a portion of the plurality of WDM wavelengths.37. The method of claim 26, wherein at least a portion of the amplifierassembly includes a dispersion compensating fiber.
 38. The method ofclaim 37, wherein at least a portion of the dispersion compensatingfiber has a magnitude of dispersion of at least 50 ps/(nm)(km) for atleast a portion of the plurality of WDM wavelengths.
 39. A method ofcommunicating WDM wavelengths in a broadband communication system,comprising: receiving a plurality of WDM wavelengths along atransmission line, at least a portion of the transmission line having adifferent sign of dispersion for at least a portion of the plurality ofWDM wavelengths; amplifying at least a portion of the plurality of WDMwavelengths with a Raman amplifier assembly tat includes a serialcombination of a distributed Raman amplifier and a discrete Ramanamplifier to create a plurality of amplified WDM wavelengths; andreceiving the plurality of amplified WDM wavelengths at a receiverassembly; wherein a majority of the plurality of WDM wavelengthsreceived by each of the distributed Raman amplifier and the discreteRaman amplifier are also received by the other of the distributed Ramanamplifier and the discrete Raman amplifier, and wherein all wavelengthsamplified by the discrete Raman amplifier are received by the same gainmedium within the discrete Raman amplifier.
 40. The method of claim 39,wherein at least a portion of the transmission line has a magnitude ofdispersion of at least 5 ps/(nm)(km) for substantially all of theplurality of WDM wavelengths.
 41. The method of claim 39, wherein thetransmission line has a magnitude of dispersion of less than 5ps/(nm)(km) for at least a portion of the plurality of WDM wavelengths.42. The method of claim 39, wherein the transmission line includes atleast two fibers with a different sign of dispersion for at least aportion of the plurality of WDM wavelengths.
 43. The method of claim 39,wherein the fibers with a different sign of dispersion are splicedtogether to provide locally high dispersion and globally low dispersion.44. The method of claim 39, wherein at least a portion of the WDMwavelengths are in the wavelength range of 1530 to 1570 nm.
 45. Themethod of claim 39, wherein at least a portion of the WDM wavelengthsare in the wavelength range of 1570 to 1630 nm.
 46. The method of claim39, wherein a first portion of the WDM wavelengths is in the wavelengthrange of 1530 to 1570 nm and a second portion of the WDM wavelengths isin the wavelength range of 1570 to 1630 nm.
 47. A multi-stage opticalamplifier system, comprising: a plurality of transmitters that produce aplurality of WDM wavelengths; a multi-stage optical amplifier including:a Raman amplifier assembly including a distributed Raman amplifier and adiscrete Raman amplifier, at least a portion of the amplifier assemblyhaving a dispersion compensating fiber with a magnitude of dispersion ofat least 50 ps/(nm)(km) for at least a portion of the plurality of WDMwavelengths; and a plurality of receivers coupled to the multi-stageoptical amplifier.
 48. The system of claim 47, wherein at least aportion of the WDM wavelengths are in the wavelength range of 1530 to1570 nm.
 49. The system of claim 47, wherein at least a portion of theWDM wavelengths are in the wavelength range of 1570 to 1630 nm.
 50. Thesystem of claim 47, wherein a first portion of the WDM wavelengths is inthe wavelength range of 1530 to 1570 nm and a second portion of the WDMwavelengths is in the wavelength range of 1570 to 1630 nm.
 51. Thesystem of claim 47, wherein the system includes a transmission line witha magnitude of dispersion of at least 5 ps/(nm)(km) for substantiallyall of the plurality of WDM wavelengths.
 52. The system of claim 47,wherein the system includes a transmission line with a magnitude ofdispersion in the range of 1-5 ps/(nm)(km) for at least a portion of theplurality of WDM wavelengths.
 53. The system of claim 47, wherein thesystem includes a transmission line with a magnitude of dispersion lessthan 1 ps/(nm)(km) for at least a portion of the plurality of WDMwavelengths.
 54. A multi-stage optical amplifier system, comprising: aplurality of transmitters that produce a plurality of WDM wavelengths; atransmission line, at least a portion of the transmission line having amagnitude of dispersion of at least 5 ps/(nm)(km) for at least a portionof the plurality of WDM wavelengths; a multi-stage optical amplifierincluding, a Raman amplifier assembly including a serial combination ofa distributed Raman amplifier and a discrete Raman amplifier, wherein amajority of the plurality of WDM wavelengths received by each of thedistributed Raman amplifier and the discrete Raman amplifier are alsoreceived by the other of the distributed Raman amplifier and thediscrete Raman amplifier, and wherein all wavelengths amplified by thediscrete Raman amplifier are received by the same gain medium within thediscrete Raman amplifier; and a plurality of receivers coupled to themulti-stage optical amplifier.
 55. The system of claim 54, wherein atleast a portion of the WDM wavelengths are in the wavelength range of1530 to 1570 nm.
 56. The system of claim 54, wherein at least a portionof the WDM wavelengths are in the wavelength range of 1570 to 1630 nm.57. The system of claim 54, wherein a first portion of the WDMwavelengths is in the wavelength range of 1530 to 1570 nm and a secondportion of the WDM wavelengths is in the wavelength range of 1570 to1630 nm.
 58. The system of claim 54, wherein at least a portion of theRaman amplifier assembly includes a dispersion compensating fiber. 59.The system of claim 58, wherein at least a portion of the dispersioncompensating fiber has a magnitude of dispersion of at least 50ps/(nm)(km) for at least a portion of the plurality of WDM wavelengths.60. A multi-stage optical amplifier system, comprising: a plurality oftransmitters that produce a plurality of WDM wavelengths; a transmissionline, at least a portion of the transmission line having a magnitude ofdispersion of less than 5 ps/(nm)(km) for at least a portion of theplurality of WDM wavelengths; a multi-stage optical amplifier including,a Raman amplifier assembly including a serial combination of adistributed Raman amplifier and a discrete Raman amplifier, wherein amajority of the plurality of WDM wavelengths received by each of thedistributed Raman amplifier and the discrete Raman amplifier are alsoreceived by the other of the distributed Raman amplifier and thediscrete Raman amplifier, and wherein all wavelengths amplified by thediscrete Raman amplifier are received by the same gain medium within thediscrete Raman amplifier; and a plurality of receivers coupled to themulti-stage optical amplifier.
 61. The system of claim 60, wherein atleast a portion of the WDM wavelengths are in the wavelength range of1530 to 1570 nm.
 62. The system of claim 60, wherein at least a portionof the WDM wavelengths are in the wavelength range of 1570 to 1630 nm.63. The system of claim 60, wherein a first portion of the WDMwavelengths is in the wavelength range of 1530 to 1570 nm and a secondportion of the WDM wavelengths is in the wavelength range of 1570 to1630 nm.
 64. The system of claim 60, wherein at least a portion of theRaman amplifier assembly includes a dispersion compensating fiber. 65.The system of claim 64, wherein at least a portion of the dispersioncompensating fiber has a magnitude of dispersion of at least 50ps/(nm)(km) for at least a portion of the plurality of WDM wavelengths.66. A multi-stage optical amplifier system, comprising: a plurality oftransmitters that produce a plurality of WDM wavelengths; a multi-stageoptical amplifier including, a Raman amplifier assembly including a gaincontrol device and a serial combination of a distributed Raman amplifierand a discrete Raman amplifier, wherein a majority of the plurality ofWDM wavelengths received by each of the distributed Raman amplifier andthe discrete Raman amplifier are also received by the other of thedistributed Raman amplifier and the discrete Raman amplifier, andwherein all wavelengths amplified by the discrete Raman amplifier arereceived by the same gain medium within the discrete Raman amplifier;and a plurality of receivers coupled to the multi-stage opticalamplifier.
 67. The system of claim 66, wherein at least a portion of theWDM wavelengths are in the wavelength range of 1530 to 1570 nm.
 68. Thesystem of claim 66, wherein at least a portion of the WDM wavelengthsare in the wavelength range of 1570 to 1630 nm.
 69. The system of claim66, wherein a first portion of the WDM wavelengths is in the wavelengthrange of 1530 to 1570 nm and a second portion of the WDM wavelengths isin the wavelength range of 1570 to 1630 nm.
 70. The system of claim 66,wherein at least a portion of the Raman amplifier assembly is adispersion compensating fiber.
 71. The system of claim 70, wherein atleast a portion of the dispersion compensating fiber has a magnitude ofat least 50 ps/(nm)(km) for at least a portion of the plurality of WDMwavelengths.
 72. The system of claim 66, wherein the gain control deviceincludes at least one adjustable gain flattening filter.
 73. The systemof claim 66, wherein the gain control device includes at least one longperiod grating.
 74. The system of claim 66, wherein the gain controldevice includes at least one cascaded Mach-Zehnder filter.
 75. Thesystem of claim 66, wherein the gain control device includes at leastone acousto-optic filter device.
 76. The method of claim 8, wherein thediscrete Raman amplifier receives the majority of the plurality of WDMwavelengths from the distributed Raman amplifier.
 77. The method ofclaim 1, wherein the distributed Raman amplifier comprises a gain fiberhaving a zero dispersion wavelength that is shorter than substantiallyall of the plurality of WDM wavelengths.
 78. The method of claim 8,wherein the transmission line has a magnitude of dispersion of at least5 ps/(nm)(km) for substantially all of the plurality of WDM wavelengths.79. The method of claim 26, wherein the distributed Raman amplifiercomprises a gain fiber having a zero dispersion wavelength that isshorter than substantially all of the plurality of WDM wavelengths. 80.The system of claim 47, wherein the distributed Raman amplifiercomprises a gain fiber having a zero dispersion wavelength that isshorter than substantially all of the plurality of WDM wavelengths. 81.A method of communicating multiple wavelength signals in a broadbandcommunication system, comprising: receiving a plurality of wavelengthsignals at a Raman amplifier assembly; amplifying at least a portion ofthe plurality of wavelength signals to create a plurality of amplifiedwavelength signals with a Raman amplifier assembly that includes acombination of a distributed Raman amplifier and a discrete Ramanamplifier, wherein at least a majority of the plurality of wavelengthsignals received by each of the distributed Raman amplifier and thediscrete Raman amplifier are also received by the other of thedistributed Raman amplifier and the discrete Raman amplifier; at leastone of the distributed Raman amplifier and the discrete Raman amplifierincludes a dispersion compensating fiber; and wherein at least amajority of the pump wavelengths that provide gain to at least some ofthe plurality of wavelength signals in the discrete Raman amplifier areshorter than all of the plurality of wavelength signals amplified by thediscrete Raman amplifier.
 82. The method of claim 81, wherein allwavelengths amplified by the discrete Raman amplifier are received bythe same gain medium within the discrete Raman amplifier.
 83. The methodof claim 81, wherein the dispersion compensating fiber comprises amagnitude of dispersion of at least 50 ps/nm km for at least a portionof the plurality of wavelength signals.